1. Field of the Invention
The present invention relates to manufacturing of integrated circuits. In particular, this invention relates to the removal of copper oxides from integrated interconnects by utilizing a high intensity UV light source.
2. Description of the Related Art
Copper thin films are currently being used as interconnection materials in semiconductor manufacturing. As compared to aluminum, a traditionally used material, copper has more advantages which are critical for improving integrated circuit performance. First, copper has a much lower sheet resistivity than aluminum. Thus, for carrying the same amount of current flow, a copper line can be made narrower and thinner than a line made of aluminum. Using copper, then, allows for a higher integration density. Also, narrower and thinner conductive lines decrease the inter-level and inter-line capacitance, which leads to a higher speed and less cross-talk for the circuit. Moreover, copper has a better electromigration resistance than aluminum. Therefore, as metal lines are made thinner and circuitry becomes more densely packed, copper provides higher reliability when used in integrated circuits.
Typically, several interconnect levels are employed in an integrated circuit. Low contact resistance, also known as via resistance, to and between interconnection levels is required.
However, during fabrication processes, a copper surface readily oxidizes even in the air, forming copper oxides, such us Cu2O and CuO. These oxides form a high resistance layer between two interlevel copper lines, which, as known by those skilled in the art, would slow down the circuit significantly.
It is necessary to remove the insulating oxide layer from the copper surface before making a connection with a subsequent copper layer.
It is thus an objective of the present invention to provide a device which can be used to efficiently remove oxides from a copper surface. It is another objective of the present invention to provide a copper oxide removal process by using the device, and integrating the process into manufacturing of interconnect levels.
In accordance with one aspect of the present invention, the device for removing copper oxide is a semiconductor reaction chamber which comprises a high intensity UV light source, a means for holding one or more semiconductor wafers inside the chamber, and a means for providing a non-oxidation environment in the chamber.
The high intensity UV light source is made of at least one array of high pressure, hollow cathode microdischarge devices which are fabricated on a semiconductor wafer. The UV light source radiates light with a wavelength preferably lower than 468 nm, to photoreduce the copper oxide on the semiconductor wafer. The total area of the light source is preferably larger than the wafer area being processed.
The reaction chamber can be made either as a single wafer or a multiple wafer chamber. The wafer holding means is preferably a moving part, so that the copper oxides can be uniformly photoreduced across the wafer or wafers.
In order to prevent the copper surface from further oxidation, a non-oxidizing environment is obtained by flowing a non-oxidizing gas during the photoreduction process. The gas can be selected from hydrogen, ammonia, nitrogen, neon, or other non-oxidizing gases.